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Ghosh SK, He L, Tang Z, Comito RJ. Selective and Functional-Group-Tolerant Photoalkylation of Imines by Energy-Transfer Photocatalysis. J Org Chem 2023; 88:15209-15217. [PMID: 37875007 DOI: 10.1021/acs.joc.3c01722] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2023]
Abstract
Basic amines show broad bioactivity and remain a promising source of new medicines. The direct photoalkylation of imines offers a promising strategy for complex amines. However, the lack of efficient imine photoreactivity hinders this reaction and remains a fundamental limitation in organic photochemistry. We report an efficient photoalkylation of imines that provides primary amines directly without protecting or leaving groups. The transformation effects C-H addition across N-H imines under energy-transfer photocatalysis by a ketone. Our method is distinguished from organometallic, metal-catalyzed, and photoredox approaches to imine alkylation by its lack of protecting groups and its broad scope, which includes unactivated alkanes, protic substrates, basic amines, heterocycles, and ketone imines. We highlight this scope through the condensation and alkylation of two pharmaceutical ketones, providing complex amines succinctly. Our mechanistic analysis supports a three-step process, involving hydrogen-atom transfer to an imine triplet excited state, intersystem crossing, and radical recombination, with photocatalytic enhancement through energy transfer. We further show that N-H imines are more photoreactive than N-substituted imines, a distinction partially explained by sterics and side reactions. To fully explain this distinction, we introduce the thermodynamic parameter excited-state hydrogen-atom affinity, which is highly effective at predicting the photoreactivity of imines.
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Affiliation(s)
- Subrata K Ghosh
- The University of Houston, 4800 Calhoun Road, Houston, Texas 77004, United States
| | - Lizhe He
- The University of Houston, 4800 Calhoun Road, Houston, Texas 77004, United States
| | - Zilu Tang
- The University of Houston, 4800 Calhoun Road, Houston, Texas 77004, United States
| | - Robert J Comito
- The University of Houston, 4800 Calhoun Road, Houston, Texas 77004, United States
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2
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Oelgemöller M, Hoffmann N. Studies in organic and physical photochemistry - an interdisciplinary approach. Org Biomol Chem 2016; 14:7392-442. [PMID: 27381273 DOI: 10.1039/c6ob00842a] [Citation(s) in RCA: 57] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Traditionally, organic photochemistry when applied to synthesis strongly interacts with physical chemistry. The aim of this review is to illustrate this very fruitful interdisciplinary approach and cooperation. A profound understanding of the photochemical reactivity and reaction mechanisms is particularly helpful for optimization and application of these reactions. Some typical reactions and particular aspects are reported such as the Norrish-Type II reaction and the Yang cyclization and related transformations, the [2 + 2] photocycloadditions, particularly the Paternò-Büchi reaction, photochemical electron transfer induced transformations, different kinds of catalytic reactions such as photoredox catalysis for organic synthesis and photooxygenation are discussed. Particular aspects such as the structure and reactivity of aryl cations, photochemical reactions in the crystalline state, chiral memory, different mechanisms of hydrogen transfer in photochemical reactions or fundamental aspects of stereoselectivity are discussed. Photochemical reactions are also investigated in the context of chemical engineering. Particularly, continuous flow reactors are of interest. Novel reactor systems are developed and modeling of photochemical transformations and different reactors play a key role in such studies. This research domain builds a bridge between fundamental studies of organic photochemical reactions and their industrial application.
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Affiliation(s)
- Michael Oelgemöller
- James Cook University, College of Science and Engineering, Townsville, QLD 4811, Australia.
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3
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Demeter A, Horváth K, Böőr K, Molnár L, Soós T, Lendvay G. Substituent Effect on the Photoreduction Kinetics of Benzophenone. J Phys Chem A 2013; 117:10196-210. [DOI: 10.1021/jp406269e] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Affiliation(s)
- Attila Demeter
- Institute
of Materials and Environmental Chemistry, ‡Institute of Organic
Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, 1025 Budapest, Pusztaszeri út 59-67, Hungary
| | - Klaudia Horváth
- Institute
of Materials and Environmental Chemistry, ‡Institute of Organic
Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, 1025 Budapest, Pusztaszeri út 59-67, Hungary
| | - Katalin Böőr
- Institute
of Materials and Environmental Chemistry, ‡Institute of Organic
Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, 1025 Budapest, Pusztaszeri út 59-67, Hungary
| | - Laura Molnár
- Institute
of Materials and Environmental Chemistry, ‡Institute of Organic
Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, 1025 Budapest, Pusztaszeri út 59-67, Hungary
| | - Tibor Soós
- Institute
of Materials and Environmental Chemistry, ‡Institute of Organic
Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, 1025 Budapest, Pusztaszeri út 59-67, Hungary
| | - György Lendvay
- Institute
of Materials and Environmental Chemistry, ‡Institute of Organic
Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, 1025 Budapest, Pusztaszeri út 59-67, Hungary
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4
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RAISSI HEIDAR, FARZAD FARZANEH, FARSI HOSSEIN. THEORETICAL INVESTIGATION OF SUBSTITUTION EFFECT ON THE PROTON TRANSFER MECHANISM IN 3-MERCAPTO-PROPENETHIAL. JOURNAL OF THEORETICAL & COMPUTATIONAL CHEMISTRY 2013. [DOI: 10.1142/s0219633613500454] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
We present detailed theoretical studies of the proton transfer (PT) in the 3-Mercapto-propenethial (MP) and in some of its derivatives. The effect of substitution on the transition state structures corresponding to the PT in R2 or R1(3) positions is studied by using B3LYP/6-311++G** level of theory in gas phase and water solution. The following substituents have been taken into consideration: Cl, F, OH, SH, OCH3, SCH3, CHO, NO2, CCH and OCF3 . For the different derivatives of 3-MP, we have computed geometries and potential energy curves for the intramolecular PT in their ground. Also, the excited-state properties of intramolecular hydrogen bonding in substituted systems have been investigated theoretically using the time-dependent density functional theory method. The π-electron delocalization parameter (Q) and HOMA index as a geometrical indicator of a local aromaticity are investigated. Natural bond orbital (NBO) analysis was also performed for better understanding the nature of intramolecular interactions. The results of analysis by Quantum theory of "Atoms in Molecules" and NBO method fairly support the DFT results. Correlations between the PT reaction barrier versus topological parameters, ν(S–H) and γ(S–H) are also probed. The obtained results showed a strong influence of the R substituent on the PT reaction barrier changes. Numerous correlations between topological, geometrical, thermodynamic properties and energetic parameters were also found.
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Affiliation(s)
- HEIDAR RAISSI
- Chemistry Department, Birjand University, Birjand, Iran
| | | | - HOSSEIN FARSI
- Chemistry Department, Birjand University, Birjand, Iran
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5
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Firme CL, Garden SJ, de Lucas NC, Nicodem DE, Correa RJ. Theoretical Study of Photochemical Hydrogen Abstraction by Triplet Aliphatic Carbonyls by Using Density Functional Theory. J Phys Chem A 2013; 117:439-50. [DOI: 10.1021/jp307505e] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Affiliation(s)
- Caio L. Firme
- Universidade Federal do Rio Grande do Norte, Instituto de Química,
Av. Salgado Filho, s/n, Lagoa Nova, Natal/RN, CEP 59072-970, Brazil
| | - Simon J. Garden
- Instituto de Química,
Universidade Federal do Rio de Janeiro, Cidade Universitária, Ilha do Fundão, Centro de Tecnologia, Bloco A, Rio de Janeiro,
RJ, CEP 21949-900, Brazil
| | - Nanci C. de Lucas
- Instituto de Química,
Universidade Federal do Rio de Janeiro, Cidade Universitária, Ilha do Fundão, Centro de Tecnologia, Bloco A, Rio de Janeiro,
RJ, CEP 21949-900, Brazil
| | - David E. Nicodem
- Instituto de Química,
Universidade Federal do Rio de Janeiro, Cidade Universitária, Ilha do Fundão, Centro de Tecnologia, Bloco A, Rio de Janeiro,
RJ, CEP 21949-900, Brazil
| | - Rodrigo J. Correa
- Instituto de Química,
Universidade Federal do Rio de Janeiro, Cidade Universitária, Ilha do Fundão, Centro de Tecnologia, Bloco A, Rio de Janeiro,
RJ, CEP 21949-900, Brazil
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6
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Zhu X, Li W, Yan H, Zhong R. Triplet phenacylimidazoliums-catalyzed photocycloaddition of 1,4-dihydropyridines: An experimental and theoretical study. J Photochem Photobiol A Chem 2012. [DOI: 10.1016/j.jphotochem.2012.05.013] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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7
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Mechanism of the intramolecular hydrogen transfer reaction at ground and excited state of tert-butyl radical: An ESR and DFT study. J Mol Struct 2012. [DOI: 10.1016/j.molstruc.2012.04.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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8
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Yabuno Y, Hiraga Y, Takagi R, Abe M. Concentration and Temperature Dependency of Regio- and Stereoselectivity in a Photochemical [2 + 2] Cycloaddition Reaction (the Paternò−Büchi Reaction): Origin of the Hydroxy-Group Directivity. J Am Chem Soc 2011; 133:2592-604. [DOI: 10.1021/ja1088524] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Affiliation(s)
- Youhei Yabuno
- Department of Chemistry, Graduate School of Science, Hiroshima University (HIRODAI), 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan, and
| | - Yoshikazu Hiraga
- Department of Chemistry, Graduate School of Science, Hiroshima University (HIRODAI), 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan, and
| | - Ryukichi Takagi
- Department of Chemistry, Graduate School of Science, Hiroshima University (HIRODAI), 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan, and
| | - Manabu Abe
- Department of Chemistry, Graduate School of Science, Hiroshima University (HIRODAI), 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan, and
- Japan Science and Technology Agency, CREST, 5 Sanbancho, Chiyodaku, Tokyo, 102-0075, Japan
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9
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Lewandowska A, Hug GL, Hörner G, Pogocki D, Kazmierczak F, Marciniak B. Intramolecular H-atom transfer reactions in rigid peptides — Correlated solvent and structural effects. CAN J CHEM 2011. [DOI: 10.1139/v10-110] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The rates and the mechanism of intramolecular hydrogen-atom transfer across the rigid diketopiperazine spacer in two epimeric benzophenone–tyrosine dyads were studied by nanosecond laser flash photolysis in 12 non-protic and protic solvents. Effects of the stereochemistry on the ground-state structures and conformational equilibria and dynamics have been addressed by means of NMR-based population analysis and long-term molecular-dynamics simulations. The excited triplet state of the benzophenone is found to be quenched intramolecularly by the remote phenol moiety with rates that are highly dependent on the solvent and on the relative benzophenone–phenol orientation. In agreement with previous studies, the kinetic diversity, with rates ranging from <105 s−1 to 2 × 107 s−1, can be attributed to retarding effects of the bulk viscosity and to effects of specific solvation, which can be both rate retarding and rate accelerating. As an extension of the previous knowledge, however, the phenomenology of the kinetic solvent effects, that is, the nature of the predominating solvent parameter and its absolute impact on the reactivity, is found to be highly correlated with structural effects.
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Affiliation(s)
- Anna Lewandowska
- Faculty of Chemistry, Adam Mickiewicz University, 60-780 Poznan, Poland
- Radiation Laboratory, University of Notre Dame, Notre Dame, IN 46556, USA
- Faculty of Biology and Agriculture, University of Rzeszow, 35-601 Rzeszow, Poland
- Institut für Chemie, Technische Universität Berlin, 10623 Berlin, Germany
- Centre of Radiation Research and Technology, Institute of Nuclear Chemistry and Technology, 03-195 Warsaw, Poland
| | - Gordon L. Hug
- Faculty of Chemistry, Adam Mickiewicz University, 60-780 Poznan, Poland
- Radiation Laboratory, University of Notre Dame, Notre Dame, IN 46556, USA
- Faculty of Biology and Agriculture, University of Rzeszow, 35-601 Rzeszow, Poland
- Institut für Chemie, Technische Universität Berlin, 10623 Berlin, Germany
- Centre of Radiation Research and Technology, Institute of Nuclear Chemistry and Technology, 03-195 Warsaw, Poland
| | - Gerald Hörner
- Faculty of Chemistry, Adam Mickiewicz University, 60-780 Poznan, Poland
- Radiation Laboratory, University of Notre Dame, Notre Dame, IN 46556, USA
- Faculty of Biology and Agriculture, University of Rzeszow, 35-601 Rzeszow, Poland
- Institut für Chemie, Technische Universität Berlin, 10623 Berlin, Germany
- Centre of Radiation Research and Technology, Institute of Nuclear Chemistry and Technology, 03-195 Warsaw, Poland
| | - Dariusz Pogocki
- Faculty of Chemistry, Adam Mickiewicz University, 60-780 Poznan, Poland
- Radiation Laboratory, University of Notre Dame, Notre Dame, IN 46556, USA
- Faculty of Biology and Agriculture, University of Rzeszow, 35-601 Rzeszow, Poland
- Institut für Chemie, Technische Universität Berlin, 10623 Berlin, Germany
- Centre of Radiation Research and Technology, Institute of Nuclear Chemistry and Technology, 03-195 Warsaw, Poland
| | - Franciszek Kazmierczak
- Faculty of Chemistry, Adam Mickiewicz University, 60-780 Poznan, Poland
- Radiation Laboratory, University of Notre Dame, Notre Dame, IN 46556, USA
- Faculty of Biology and Agriculture, University of Rzeszow, 35-601 Rzeszow, Poland
- Institut für Chemie, Technische Universität Berlin, 10623 Berlin, Germany
- Centre of Radiation Research and Technology, Institute of Nuclear Chemistry and Technology, 03-195 Warsaw, Poland
| | - Bronislaw Marciniak
- Faculty of Chemistry, Adam Mickiewicz University, 60-780 Poznan, Poland
- Radiation Laboratory, University of Notre Dame, Notre Dame, IN 46556, USA
- Faculty of Biology and Agriculture, University of Rzeszow, 35-601 Rzeszow, Poland
- Institut für Chemie, Technische Universität Berlin, 10623 Berlin, Germany
- Centre of Radiation Research and Technology, Institute of Nuclear Chemistry and Technology, 03-195 Warsaw, Poland
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10
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Meyer R, Zhang X, Nau WM. Effect of bridgehead substitution on the fluorescence quenching of 2,3-diazabicyclo[2.2.2]oct-2-enes by solvents and antioxidants. Photochem Photobiol Sci 2009; 8:1694-700. [PMID: 20024166 DOI: 10.1039/b9pp00081j] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Azoalkanes of the 2,3-diazabicyclo[2.2.2]-oct-2-ene type have been introduced as probes for antioxidants in homogeneous solution as well as in liposomes and micelles. The bimolecular fluorescence quenching of the bridgehead dichloro-substituted 1,4-dichloro-2,3-diazabicyclo[2.2.2]-oct-2-ene (3) was compared with that of the parent compound 2,3-diazabicyclo[2.2.2]-oct-2-ene (1) and the bridgehead-dialkylated compound 4-methyl-1-isopropyl-2,3-diazabicyclo[2.2.2]-oct-2-ene (2). Compound 3 showed a more efficient fluorescence quenching in C-H containing solvents (e.g., in n-hexane: 30 ns for 3 versus 340 ns for 1 and 770 ns for 2), but a less efficient quenching in aqueous solution (e.g., in deaerated H(2)O: 485 ns for 3 versus 420 ns for 1 and 340 ns for 2), and also by molecular oxygen (k(q)/10(9) M(-1) s(-1) = 0.32 for versus 2.5 for 1 and 1.9 for 2). Towards low-molecular weight antioxidants, compound 3 showed a significantly higher reactivity (e.g., for reduced glutathione: k(q)/10(9) M(-1) s(-1) = 1.8 for 3 versus 0.82 for 1 and 0.39 for 2), at the expense of a lower differentiation between the investigated antioxidants (lower selectivity). The increased reactivity of 3 and lower, as well as qualitatively different, selectivity is attributed to a combination of factors, most importantly the slightly increased excitation energy of 3 and its lower excited-state nucleophilicity. The latter was independently corroborated, besides its longer fluorescence lifetime in aqueous solution, through the trends in quenching rate constants of the azoalkanes 1-3 towards electron-deficient versus electron-rich lactone antioxidants of the benzofuranone type. While common inorganic buffer constituents caused no fluorescence quenching, significant quenching was observed, as a curiosity, for hydrogencarbonate (k(q)/10(6) M(-1) s(-1) = 1.7 for 3 versus 2.4 for 1 and 0.45 for 2), with a fully manifested kinetic deuterium isotope effect (k(q)(H(2)O)/k(q)(D(2)O) = 12) for 3.
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Affiliation(s)
- Roland Meyer
- School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, D-28759, Bremen, Germany
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11
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Hörner G, Hug G, Pogocki D, Filipiak P, Bauer W, Grohmann A, Lämmermann A, Pedzinski T, Marciniak B. Head-to-Tail Interactions in Tyrosine/Benzophenone Dyads in the Ground and the Excited State: NMR and Laser Flash Photolysis Studies. Chemistry 2008; 14:7913-29. [DOI: 10.1002/chem.200800315] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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12
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Investigations on the fluorescence quenching of 2,3-diazabicyclo[2.2.2]oct-2-ene by certain flavonoids. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 2008; 91:143-50. [DOI: 10.1016/j.jphotobiol.2008.03.003] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2007] [Revised: 03/08/2008] [Accepted: 03/11/2008] [Indexed: 11/22/2022]
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13
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Anbazhagan V, Kandavelu V, Kathiravan A, Renganathan R. Investigation on the fluorescence quenching of 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) by certain estrogens and catechols. J Photochem Photobiol A Chem 2008. [DOI: 10.1016/j.jphotochem.2007.06.026] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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14
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Koner AL, Pischel U, Nau WM. Kinetic Solvent Effects on Hydrogen Abstraction Reactions. Org Lett 2007; 9:2899-902. [PMID: 17580891 DOI: 10.1021/ol071165g] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Kinetic solvent effects on hydrogen abstractions, namely, acceleration in nonpolar solvents, have been presumed to be restricted to O-H hydrogen donors. We demonstrate that also abstractions from C-H and even Sn-H bonds by cumyloxyl radicals and n,pi*-excited 2,3-diazabicyclo[2.2.2]oct-2-ene are fastest in the gas phase and nonpolar solvents but slowest in acetonitrile. Accordingly, solvent effects on hydrogen abstractions are more general, presumably due to stabilization of the reactive oxygen or nitrogen species in polar solvents.
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Affiliation(s)
- Apurba L Koner
- School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, D-28759 Bremen, Germany
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15
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Lalevée J, Gigmes D, Bertin D, Graff B, Allonas X, Fouassier J. Comparative reactivity of aminyl and aminoalkyl radicals. Chem Phys Lett 2007. [DOI: 10.1016/j.cplett.2007.03.029] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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16
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Lundgren CV, Koner AL, Tinkl M, Pischel U, Nau WM. Reaction of Singlet-Excited 2,3-Diazabicyclo[2.2.2]oct-2-ene andtert-Butoxyl Radicals with Aryl-Substituted Benzofuranones. J Org Chem 2006; 71:1977-83. [PMID: 16496983 DOI: 10.1021/jo052440k] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
5,7-Di-tert-butyl-3-aryl-3H-benzofuran-2-ones are lactones with potential antioxidant activity, owing to their abstractable benzylic C-H hydrogens. The fluorescence quenching of the azoalkane 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO), an established probe for the hydrogen-donor propensity of chain-breaking antioxidants, was investigated for 16 aryl-substituted benzofuranone derivatives [m,m-(CF3)2, p-CN, m-CN, p-CF3, p-COOCH3, m-CF3, p-Cl, p-F, H, m-CH3, p-CH3, m,p-(CH3)2, p-OCH3, o-CH3, o-CF3, o,m-(CH3)2]. Analysis of the rate data in terms of a linear free energy relationship yielded a reaction constant of rho = +0.35. This implies that n,pi*-excited DBO acts as nucleophilic species. In contrast, hydrogen abstraction of tert-butoxyl radicals from the benzofuranones was accelerated by electron-donating substituents (rho = -0.23), in conformity with the electrophilic character of oxygen-centered alkoxyl radicals. Possible implications for the optimization of the hydrogen-donor propensity of antioxidants through structural variation are discussed.
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Affiliation(s)
- Cecilia Vannesjö Lundgren
- School of Engineering and Science, International University Bremen, Campus Ring 1, D-28759 Bremen, Germany
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17
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Pischel U, Patra D, Koner AL, Nau WM. Investigation of Polar and Stereoelectronic Effects on Pure Excited-state Hydrogen Atom Abstractions from Phenols and Alkylbenzenes†. Photochem Photobiol 2006; 82:310-7. [PMID: 15882091 DOI: 10.1562/2005-02-07-ra-434] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The fluorescence quenching of singlet-excited 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) by 22 phenols and 12 alkylbenzenes has been investigated. Quenching rate constants in acetonitrile are in the range of 10(8)-10(9) M(-1)s(-1) for phenols and 10(5)-10(6) M(-1)s(-1) for alkylbenzenes. In contrast to the quenching of triplet-excited benzophenone, no exciplexes are involved, so that a pure hydrogen atom transfer is proposed as quenching mechanism. This is supported by (1) pronounced deuterium isotope effects (kH/kD ca 4-6), which were observed for phenols and alkylbenzenes, and (2) a strongly endergonic thermodynamics for charge transfer processes (electron transfer, exciplex formation). In the case of phenols, linear free energy relationships applied, which led to a reaction constant of rho = -0.40, suggesting a lower electrophilicity of singlet-excited DBO than that of triplet-excited ketones and alkoxyl radicals. The reactivity of singlet-excited DBO exposes statistical, steric, polar and stereoelectronic effects on the hydrogen atom abstraction process in the absence of complications because of competitive exciplex formation.
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Affiliation(s)
- Uwe Pischel
- REQUIMTE/Department of Chemistry, University of Porto, Porto, Portugal.
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Marquez C, Pischel U, Nau WM. Selective fluorescence quenching of 2,3-diazabicyclo[2.2.2]oct-2-ene by nucleotides. Org Lett 2004; 5:3911-4. [PMID: 14535741 DOI: 10.1021/ol035454q] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
[reaction: see text] The fluorescence quenching of 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) by nucleotides has been studied. The quenching mechanism was analyzed on the basis of deuterium isotope effects, tendencies for exciplex formation, and the quenching efficiency in the presence of a molecular container (cucurbit[7]uril). Exciplex-induced quenching appears to prevail for adenosine, cytidine, and uridine, while hydrogen abstraction becomes competitive for thymidine and guanosine. Compared to other fluorescent probes, DBO responds very selectively to the type of nucleotide.
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Affiliation(s)
- Cesar Marquez
- School of Engineering and Science, International University Bremen, Campus Ring 1, D-28759 Bremen, Germany
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Klapstein D, Pischel U, Nau WM. Quenching of n,pi*-excited states in the gas phase: variations in absolute reactivity and selectivity. J Am Chem Soc 2002; 124:11349-57. [PMID: 12236750 DOI: 10.1021/ja020400h] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The quenching of the n,pi*-excited azoalkane 2,3-diazabicyclo[2.2.2]oct-2-ene by 19 heteroatom-containing electron and hydrogen donors, that is, amines, sulfides, ethers, and alcohols, was investigated in the gas phase. Deuterium isotope effects were measured for 9 selectively deuterated derivatives. The data support the involvement of an excited charge-transfer complex, that is, an exciplex, for tertiary amines and sulfides, and a competitive direct hydrogen transfer from the C-H bonds of ethers or from the N-H or O-H bonds of secondary and primary amines or alcohols. The recently observed "inverted" solvent effect for the fluorescence quenching of azoalkanes by amines and sulfides in solution is supported by the observed rate constants in the gas phase, which are substantially larger than those in solution. A more pronounced inverted solvent effect for the weaker electron-donating sulfides and a presumably faster exciplex deactivation result in a switch-over in absolute reactivity relative to tertiary amines in the gas phase. Most importantly, the kinetic data demonstrate that the reactivity of the strongly dipolar O-H and N-H bonds in photoinduced hydrogen abstraction reactions shows a larger decrease upon solvation than that of the less polar C-H bonds. The azoalkane data are compared with previous studies on quenching of n,pi*-triplet-excited ketones in the gas phase.
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Affiliation(s)
- Dieter Klapstein
- Department of Chemistry, St. Francis Xavier University, Antigonish, Nova Scotia B2G 2W5, Canada
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